Scientists have known for a while that merely walking more can massively decrease the risk of heart disease and type 2 diabetes, but they haven't really known why. But now, by forcing healthy people to act like slobs, they're starting to reveal why walking is the best thing you can do for your body.

The reason it's tricky to work out why walking is so beneficial to those who live a sedentary lifestyle is because inactivity is tied up with other factors: poor diet, overweight, and plenty of other lifestyle problems. So to tease out why walking is beneficial, scientists from the University of Missouri flipped the problem on its head and took fit, active people, and sentenced them to bed rest, reports the New York Times.

In fact, the volunteers spent three days living their normal, active lifestyle, then were forced to cut their efforts by at least half. During the period, they had their blood sugar levels continuously monitored. "It's increasingly clear that blood sugar spikes, especially after a meal, are bad for you," says John P. Thyfault, one of the researchers, told the NYT. "Spikes and swings in blood sugar after meals have been linked to the development of heart disease and Type 2 diabetes."

Between the two periods, activity dropped from an average of over 13,000 steps a day to less than 4,300. Meanwhile, the participants ate exactly the same meals and snacks throughout.

The result? Blood sugar levels spiked more easily during the inactive days, and the spikes got more pronounced as the sedentary period went on. That's not tied up with changes in fitness, or getting fat, but is the body's natural reaction to doing less—even low-impact—exercise.

The spikes aren't hugely surprising, but they are very concerning. They suggest that even someone of a normal weight who eats a healthy diet could see dramatic spikes in blood sugar over time if they live a sedentary lifestyle—a problem that can in turn lead to early onset of type 2 diabetes and heart disease.

The moral? Move a little more: it doesn't have to be high-impact, and it needn't get in the way of your lifestyle. But get off you ass and walk a little, and you'll do your body the world of good. The average American manages less than 5,000 steps a day; ideally, they should be doing over 10,000. There's a growing body of evidence suggesting that walking really is the best exercise you can do—so do it. [New York Times; Image: Mustafa Khayat]